Police investigating the deadliest London terror attack in 12 years named the perpetrator Thursday as a 52-year-old British man, Khalid Masood.

Prime Minister Theresa May earlier revealed that Masood was once linked to violent extremism but was regarded as a “peripheral figure.” She also told Parliament he was thought to be inspired by Islamist ideology.

Police arrested eight people in raids around Britain, as an ISIS-affiliated news agency claimed that the extremist group was behind Wednesday’s outrage.

Three people died in the attack — an American man, a British woman of Spanish origin and a police officer stabbed as he defended Parliament. Another 40, many of them from other countries, were injured. Of those, 29 required hospital treatment and seven are critical, police said.

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Confirmation of the perpetrator’s identity came more than 24 hours after he launched the attack, in which he plowed a car into crowds of people on Westminster Bridge, killing two, before stabbing the police officer dead in the grounds of the UK Parliament.